The invention concerns an optical component having a guide with a ridge structure, (know as xe2x80x9cridge waveguidexe2x80x9d). The invention applies to such a guide having a curved section.
The invention also concerns a method of manufacturing such a guide.
The field of the invention is that of guides with a ridge structure, chemically etched on a substrate made of semiconductor material and having curved sections, that is to say whose orientation is not parallel to the reference crystallographic direction of the substrate.
When a guide with a ridge structure is chemically etched, the width of the base of the ridge is smaller than the width of its top face. In the case of a guide with curved sections, this difference is variable along the guide and can be accentuated at certain points on the guide. However, the variation in the width of the base of the ridge causes losses in propagation of the guided mode and a change in the effective index of the optical mode of the guide.
One solution consists consequently of seeking to keep the width of the ridge constant, even in a curve. For this purpose, it is possible for example to produce the guide by dry etching. Such a dry etching method makes it possible to produce guides with a ridge structure with a rectangular section at any point in the guide whatever the local orientation of the guide. However, such a dry etching does not make it possible to obtain a ridge structure with the same quality as that obtained by a chemical etching.
In particular, the sides of the ridge are rougher, and the irregularity can be as much as several tens of nanometers in depth.
Moreover, the etching takes longer, a few hours compared with a few minutes for chemical etching.
In addition, the stoppage of the etching is not precisely controlled as in the case of chemical etching.
The aim of the invention is to propose a chemically etched guide with a ridge structure and having a modal index controlled at any point on the guide, even in curved sections.
The invention is based on a surprising physical observation according to which, in the case of a guide with a ridge structure, the modal index is determined by the width of the base of the ridge.
The object of the invention is more particularly an optical component having at least one guide with a ridge structure obtained by chemical etching on a substrate made of semiconductor material, the ridge having a base and a top face, the guide having an outline with at least one curved section, the tangent at any point on the outline defining a local orientation of the guide, characterised in that the width of the base of the ridge is substantially controlled all along the guide and the width of the top face of the ridge varies according to the orientation of the guide with respect to the reference crystallographic direction of the substrate.
According to one application, for which it is wished to obtain a constant modal index at any point on the guide, the width of the base of the ridge is substantially constant along the curved section of the outline of the guide.
According to one characteristic, the guide is produced on a substrate made of III-V semiconductor material and has a bottom layer stopping the etching made from quaternary semiconductor material.
According to one particularity, the quaternary material is composed of indium-gallium arsenide phosphide (InGaAsP).
The present invention also concerns a method of manufacturing an optical component produced on a substrate made of semiconductor material and having a guide with a ridge structure, the guide having an outline with at least one curved section, the tangent at any point on the outline defining a local orientation of the guide, the said structure being obtained by at least one step of chemical etching through a mask defining in particular the width of the top face of the ridge, characterised in that the said width of the top face varies according to the local orientation of the guide with respect to the reference crystallographic direction of the substrate and according to the required width of the base of the ridge.
According to one characteristic, the chemical etching is effected using a selective chemical solution according to the chemical composition and the crystallographic orientation of the semiconductor materials constituting the guide with a ridge structure. For example, a solution of hydrochloric acid and orthophosphoric acid (HCl/H3PO4).